S9-Dependent Activation of 1-Nitropyrene and 3-Nitrofluoranthene in Bacterial Mutagenicity Assays
Nitro-substituted polycyclic aromatic hydrocarbons (NO2PAH) such as 1-nitropyrene (NP) and 3-nitrofluoranthene (NFA; see Fig. 1) have been detected in diesel and other combustion emissions (Nishioka et al., 1982; Gibson, 1982; Schuetzle et al., 1982). Many of these compounds are potent mutagens, and some are animal carcinogens (Hirose et al., 1984; Ohgahki et al., 1982). The mutagenicity of NO2PAH in the Ames Salmonella typhimurium plate incorporation assay is generally dependent on nitroreductase activity in the bacterial tester strains utilised (Mermelstein et al., 1981). This was shown to be the case for NP (Mermelstein et al., 1981; Ball et al., 1984a). When the bacterial tester strain was deficient in the required nitroreductase enzyme, metabolism by mammalian S9 or microsomal fractions was also able to activate this compound, although to a lesser extent (Kohan and Claxton, 1983; Ball et al, 1984a). Oxidative metabolism of NP both in vivo (Ball et al., 1984b) and in vitro (El-Bayoumy and Hecht, 1983; Ball et al., 1984a) was shown to form phenols and dihydrodiols some of which were themselves mutagenic to Salmonella. Binding to DNA, also an indication of potential for genotoxic damage, was catalysed both by reductive (Messieret al., 1981; Howard et al., 1983) and by NADPH-dependent oxidative metabolism of NP (Ball and Lewtas, 1985). Therefore both oxidative and reduc — tive pathways apppear to be capable of producing genotoxic intermediates from NP; further investigations will show whether this holds true for other NO2PAH, and what factors determine the relative importance of each route of metabolism. Thus we describe here a comparison of the activation pathways of NP and NFA (a NO2PAH which has not yet been as well characterised as NP) in the Ames assay for reversion to histidine independence in Salmonella strain TA98 and in a forward mutation to 8-azaguanine resistance in Salmonella strain TM677 (Skopek et al., 1978, modified by Goto et al., 1985).
KeywordsStrain TA98 High Pressure Liquid Chromato Ames Assay Nitroreductase Activity Strain TM677
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